In an internal combustion engine with a supercharger, in order to prevent an excessive rise in engine output power, there are provided a communication passage for connecting between the upstream and downstream sides of an exhaust gas turbine of a supercharger, and a waste gate valve for opening and closing the communication passage, wherein when supercharging pressure rises, the waste gate valve is opened to decrease the flow rate of exhaust gas passing through the exhaust gas turbine so as to prevent the supercharging pressure from rising excessively.
There has been known a technique in which provision is made for a main urging means for urging a waste gate valve in a direction downstream of an exhaust gas in accordance with rising of the supercharging pressure, and an urging force correction means for urging the waste gate valve in a direction to cancel a differential pressure between the upstream and downstream sides of the waste gate valve in accordance with the magnitude of the differential pressure, wherein surging is suppressed by counterbalancing the influence of the differential pressure between the upstream and downstream sides of the waste gate valve (see, for example, a first patent document (Japanese utility model application laid-open No. S63-82033), a second patent document (Japanese patent application laid-open No. 2002-195046), a third patent document (Japanese patent application laid-open No. H5-141258), a fourth patent document (Japanese patent application laid-open No. H3-294623) and a fifth patent document (Japanese patent application laid-open No. H1-110832).
However, a spring for urging the waste gate valve is set in such a manner that the waste gate valve is fully opened at a maximum supercharging pressure. In such a setting, when the differential pressure between the upstream and downstream sides of the waste gate valve becomes equal to or higher than a certain pressure which is even lower than the maximum supercharging pressure, the spring is gradually displaced in accordance with the increasing differential pressure, whereby the waste gate valve is caused to gradually open. As the waste gate valve is gradually opened in this manner, the amount of exhaust gas for rotating the turbine is excessively decreased, thereby making the rising of the supercharging pressure dull or gradual. As a result, the engine torque does not increase quickly, thus deteriorating driveability.